1. Field of the Invention
This invention relates to the field of pumps and more particularly to a diaphragm pump free of leakage normally attendant with debris related pump leaks.
2. Brief Description of the Prior Art
There are many applications for fluid pumps where it is desirable for the pump not to leak fluid back through the pump's outlet port when the pump is stopped. For example, machines that automatically take a patient's blood pressure inflate a blood pressure cuff with air to some predetermined pressure below 6 PSI and then very slowly deflate the cuff at a precise rate. When the inflation pump halts at the desired pressure, it should ideally not allow air in the pressurized cuff to leak back through the pump since the precise deflation rate will not be achieved, thereby resulting in an erroneous blood pressure reading.
Leak-back primarily occurs through imperfections in the pump's one-way valves that do not allow the valves to operate as perfect check-valves. The problem is more frequently seen when there is a relatively small pressure gradient from inlet to outlet such as with the case of automatic blood pressure measurement machines. These imperfections are most often small pieces of debris that are shed from the pump's diaphragm.
The diaphragm employed in many pumps being used today have a hole in their center and the diaphragm is attached to a connecting rod with a washer on each side of the diaphragm's hole with a bolt projecting through the bottom washer, diaphragm hole, top washer and which screws into the bottom of the connecting rod. The bottom washer is therefore within the pumping chamber. As the diaphragm is moved in reciprocating motion, the diaphragm must stretch and/or move with respect to the bottom washer. Since the bottom washer is typically not flexible like the diaphragm is, some shearing action takes place between the diaphragm and bottom washer with each reciprocating motion of the diaphragm. The shearing action abrades the diaphragm and small particles of the diaphragm's material are shed to within the pumping chamber and can become deposited in the check valves.
When the pump is stopped, even a small piece of debris that happens to remain on a valve's sealing surfaces will cause a leak.
Therefore, a long standing need has existed which provides a diaphragm pump free from debris related problems resulting in pump leaks and clogging of check valves.